Method of and means for recording electrical impulses and impulse record produced thereby



METHOD OF AND MEANS FOR RECORDING ELECTRICAL IMPULSES AND IMPULSE RECORD PRODUCED THEREBY A Filed Aug. 4, 1944 4 Sheets--Shee'ri l July 15 19,46 J. A. MURERCJR' v 2,404,137

INVEN'TOR: JOHN A.MAURER JR.

AGENT 'July 16, 1946.

Filed Aug. 4, 1944 4 Sheets-Sheet 2 INVENTOR:

JOHN A. MAURERJR AGENT July 16, 1946. y lJ. A;.MA'URl-:R JR 2,404,137

H OF AND MEANS FOR REGRDIN ELECTRICAL U s AND IMPULSE RECORD PRO En THEREBY Filed Aug. 4.4 1944 4 Sheets-Sheet 3 x09 j iQ I O2 l 2 Hoa. |03 |1078.

INVENTOR.'

JOHN AMAURER JR.

BY@ Maw/1% AGENT 2,404,l 37 IMPULsEs A ND IMPULSE RECORD PRODUCED THEREBY' J. A@ MAURER, JR 16 1946METHOD OF'AND MEANS FOR RECORDING ELECTRICAL 4 Sheets-Sheet 4` Filed Aug."

INVENTOR; v JOHN A, MAURERJR BY@ mm AGENT Patented July 16, h1946 METHOD OF FOR RECORDING 'ELECTRICAL IIWPULSES l.AND IMPULSE RECORD PRODUCED THEREBY John A. Maurer, Jr., New York, N. Y., assignor to J. A. Maurer, Ine., New York, N. Y., a corpora.-

tion of New York Application August 4, 1944, Serial No. 548,098

15 claims. (o1. 17e-fiona) l This invention relates to the photographic rei cording of electrical impulses on a moving lm as it is practiced, for example, in sound-on-lm recording.

By such recording, two main kinds of photographic tracks may be produced on the moving nim, namely, variable area tracks and variable .both-variable area and variable density tracks therewith. Y

More particularly, the invention is related to the production of'variable area and variable density tracks which are composed of two half-tracks int juxtaposition.v Each half-track is a, complete record of the electrical impulses, but-the Vtwo Yhalf-tracks are displaced `180 out of phase in relation to one another transversely of the film; :This kind of track is known in the art as a pushpull class A track; A

'I'he advantages of push-pull class A tracks are well known, and hence need not be stated here anew. It is likewise known that, for the rest position of the Voscillograph mirror, prints made of these tracks ordinarily have a 'comparatively Widetransparent portion in the caseof variable area tracks, and a comparatively large light transmission lin the` case cf variable density tracks. Thiscondition is unsatisfactory when the electrical impulses recorded in the tracks are .sound currents so that sound is to be reproduced from the prints, forit lthenresults in a comparatively Alarge amountrof ground noise. It is, of course, possible to employ, in the production of push-pull class A tracks, the well known electrical methods of ground noise reduction, be it the bias, or the shutter, method. But the application of either method presents certain dlcultiesand,

y,in addition; requires special equipment such as rectiers and the like.

The invention,- therefore, proposes a. method of,

and means for, producing push-pull class A tracks in-which groundnoise reduction is inherent. Its starting point is the fact that the response of ,any conventional push-pull-rreproducing system isequal to the difference in` response of the tw@ 2 photocells employed therein. 'I'he individual responses of the photocells hence may be nonlinearly related to the amplitude of the electrical impulses recorded inthe push-pull class A tracks, 5 as loingA as their ,difference is linearly related to that amplitude. Consequently,no amplitude distortion occurswl'ien the push-pull class A tracks are so produced that the two component halftracks of their prints have eachv a transparent portion, or light transmission,A which is non-linearly related to the aforementioned amplitude if only the difference of the two transparent portions, or light transmissions, is linearly related thereto. VLSuc/ h a linear relationship4 is established, according to (the. invention, when the transparent portion,l orligiht transmission, of each half-tracker; the print varies in proportion to .the square ofthe amplitude referred'to above. At the same time, alvariation of this character `2() brings it about that the value of the transparent portion, or light transmission, for the rest position of the oscillograph mirror decreases to such Ya degree that the ground noise is materially reduced when sound is reproduced from the print.

:'25 VThe invention, furthermore, provides thefollowingv methodv for recording push-pullclas's'A tracks from which prints may be madewith halftracks hai'fimgthe properties outlined at the end of the preceding paragrapil Y 1 l 30 YA nlm is mfed vertically' pastj the recording point at whichV two horizontal lines of light are produced in juxtaposition. The amount of'lig'ht flux contained in each line of light is continuously 'varied in proportion to the square of the yamplitude of the electrical impulses to be recorded, but the amount of light ilux containedV in the one line of light is varied 180 outof phase in relation to the amount of ylight `flux contained in the other line of light. When. therv'ariation .y of the two amounts of light iiux is accomplishedby varyingV the length of the two linesof, light, a variable area track is'frecorded, and when it is accomplished :by varying their intensity; a variable densityy track is recorded. f

ing. out this method. In an optical system o1' the mirror oscillo'graph type', a, screen is provided with a pair of uniformly illuminated openings, images of which are formed in the plane of a hori- 150 .zontal' slit so as to be movable by the 'vibration' of y theoscillograph mirron The twoV openingsI 'are substantially Vvtriangular and alike. fTley are 'spaced .apart horizontally, and inversely, positionedverticallyin that-the tip of the oneopenest 'ing "1s-ifa alignment Y Withthe base of! the einer PATENT fori-fica] l The invention also proposes means Vforfcarry- 3 opening, and vice versa. TheV shape of these openings is such that their effective horizontal extension or width, increases in proportion to the square of its distance from their tip. A variation in width of this character is obtained by providing each opening with one or two .edges jwhich extend from its .tip towards its base, and. whose ef- Since the edges are parabolic throughout their eiective contour, the transition between any two points thereon is a smooth one. For that reason,

part in the variationof the light `iiuxat the recording point, the use of a pair of these openings and also because each opening continuously ,takes A v in the optical system introduces no higher order harmonic.

The ground noise reduction effectedY by the 'i method and means of the present invention amounts to 3 decibelsV inthe casel of variable area tracks,'and-6 decibels the case of variable density-tracks. These resultsaresufcient to make the application ofthe electrical methods of groundY noise-reduction Vsuperfluous in a great number of practical cases. The production of push-pull `classA sound tracks with ground noise reduction hence is materially facilitated by the invention since its application requires neither special equipment, nor critical adjustment. It Ashould be noted that the terms vertica and horizontal have been -us'ed in the foregoing brief summary of the invention, and will be used throughout this specification, not in any absolute sense but merely as indicating two directions at right angles to each other, andthat choice between these terms has Ybeen determined solely by convenience in 'description and illustration.

Anvobject of the invention is the provisionof improvedpush-pull class A tracks.

ist

Another V object'of the invention'is the provision."l

of push-pullA classA sound tracks with inherent t ground noise reduction.

3 Another'object of the invention is the provision of'push-pull class A variable area tracks having 'half-tracks whoseY transparent portion varies in proportion tothesquare'of the amplitude of the electricalzimpulses recorded inv the tracks.

Another object ofthe inventionV is the pro,

vvision of push-pull class A variable density tracks having:V half-tracks whose.V light transmission Y varies in proportion to the square ofthe ampli- 4 rnlitliool 1 of producing. push-pull class A sound vtrackswith ground noise reduction which does not require special equipment. A

` Another object of the invention is'the provision of improved means for producing push- .pull ,class A sound tracks with inherenty ground noise,reduction.y `.Another object of the invention is the provision of such means which introduce no higher order harmonic. v f

Stilljothe'r objects and advantages cf the inventiorrjinclude'4 those which are hereinafter ystateo'lfor apparent, or which are incidental tothe invention.

, .'I'hejinvention will be better understood when the( following description. is considered f' with `the accompanying drawings of certain presently prefrs yof the invention is to provide ,455

shape'- and relative ferred embodiments thereof, and its scope will be pointed out in the appended claims.

In the drawings:

Fig. 1 is a diagrammatic perspective view of a variable area recording optical system in which the invention has been embodied.

Fig.-2 Yshows anl enlarged elevation ofva part of the optical system of Fig. 1, namely, a screen .provided with a pair of openings according to the invention.

y Fig. 3, which'is drawn toa somewhat larger 'scalethan'Fig 2. shows the openings of Fig. 2 related to a system of rectangular co-ordinates.

Fig. 4- is adiagrammatic representation of a print 'made from a push-pull class A variable areatrack produced by means of the openings of Fig. 2.

Figs. 5,6, 7, and 8, show in enlarged elevation modiications of the openings which may be provided in the screen of Fig. 2.

.Fig.9,. V.which 'isy drawn to .a somewhat larger scale thanFig. 8, shows the openings ofFig. 8 related toasystem of rectangular co-ordinates.

Fig. 10 is a diagrammaticy representation of a printV made from a push-pulll class. A variable area track ,produced by means of the openings of Fig. 8.

Fig. 11 is a diagrammatic perspective view of a variable density recording optical system in which the invention. has beenembodied.

Fig. 12 is a diagrammatic longitudinal section of theA optical system shown in Fig. 11', theoptical axis being represented asa straight line and an oscillograph mirror as an aperture.

Fig' 13 is acorr'esponding section in the :horizontal plane.

Fig. 14 is an enlargedfront elevationof a part of the optical system4 ofA Fig. 11. 1 Fig. 15 is a diagrammatic representation of a print made from a push-pull class A Yvariable density track produced by means of any/of the pairs lof openings shown in Figs. 2 and 5 to 8, and

Figs.. 16 Aand 17 show adaptations to a particular purpose of theopenings of Figs.. 2 land, respectively.

u Figgl shows, by .ventionmay be, embodied4 in a conventional varialolerarea recording optical/system. The optical system of Fig. 1 has a suitablelight vsource such 'as the lainent .ID of anv in candescentrlamp Lamp. iilament |0- isf imaged substantiallyon the *mirror v|2 .by the spherical 'condenser I3., and:v reimagedv .substantially in. the microscope objective |'4 by the Aspherical lens. 'I 5'. f

A. screen y2|) is. provided-with two substantially triangular'openings 2| and 22, and placed adjacent to condenser lens|3 so that openings 2 |l and 22.1are uniformly illuminated by lightfflux from lampllame'nt I0. Openings 2| and 22, which' Yare spaced apart horizontally, are alike but in- Vshape of openings 2|- and '.22 -wi'll be explained hereinafter.

'Asphericalslens 23 is placed in frontlof mirror I2 and formson a screen 24 two images 25 and 26 yof.openings 2| and 22;'"1j-'espectively.`V .'Since openings 2| and 22 areun-iformly illuminated, and since lens 23 lis spherical, images 25 and 26 are' 'two uniformly illuminated 'light spotsA whose position are'thoseA of 'openings .way of example, howthe in' 2G thus are formed inthe plane of slit'21 so as to illuminate two portions thereof. AAs seen from the recording point 30, therefore, there appear at slit 21 two horizontal' lines of light in juxtapositionk which are reproduced at recording point 30 by the microscope objective I4. Recording point 3U. is thepoint at which'the' optical axis of the system strikes the iilm 3|, and film 3I moves at recording p oint. 3E!A in a substantially ivertical di-V rection as indicated by the arrow 32.

Mirror I2 is mounted for vibration on an oscillograph galvanometer 33, or similar device'for translating electricalimpulses into mechanical vibrations. The axis 34,34 about which mirror I2 is` adapted to vibrate, extends horizontally. Whentherefore, the electrical impulses to be recorded are applied in known manner to the oscillograph 33, mirrorA I2 vibrates in accordance therewith and thereby moves images 25 and 26 vertically across the, horizontal slit 21. This movement of images 25 and 26 brings itabout that each of the two lines of light appearing at slit 21, and again at recording point 30, continuously varies in horizontalA extension, orlength, in accordance with the amplitude of the electrical impulses applied tooscillograph 33. I g

Thus.there is produced on nlm 3l as it moves vertically past recording point 30, a photographic record of the electrical impulses which arefap plied to the' oscillograph 33. vThis record is made up ofthe two variable area tracks35 and 36 in juxtaposition and, sincel the variation in length ofthe two lines of light at recording 'point 30 is continuous, each track `35and3i -is a complete .record of the electrical impulses.. However, on

account of the inverted'position `of openings 2 I and 22, track 36 is displaced y180 out of phasein relation to track 35 transversely of film l,3.I. Tracks 35 and 35 henceare thel two component half-tracks of'a push-pull class A variable area trackl 31. But track 31 is different from,l and superior to,l a conventional variable area trackv of the push-pull class A type forv the following reasons.v

Referring. for the sake of further explanation axis apaanei rebase-4|. :Edge 6,1m theether positioned vertically. in that the tip ofthe one' opening is'in alignment with the base Tof the other opening, and vice versa. i i

A speciiic property of openings 2| -and 22 which results from their. being bounded by-paarabolic edges 42 and 46, respectively, will now-be` explained with referenceto Fig. 3. In this figure, which is drawn to .a somewhat larger scalethan Fig. 2, openings 2| and `22 are related tQas-ystem of rectangular co-ordinates X-X Vand `iff-Y'. ',Ihe origin-O of this co-ordinate `system ,isthe center of the rectangle formed by the two `straight edges 40 and 44, and the two extensionspf--bases 4I and 45, respectively, between edges 40 and 414. The axis'X-X of thesystem is parallel to bases 4I and 45, and its axis Y-,-Y parallel to edges 40 'and 44. Y L

Since the length of edges 40 and 44 is V2h and that of the two extensions of bases 4I and 45 is 2d, the co-ordinates of the tips V and W of openings 2I and 22, respectively, are (d, h) and (-d, -h'), respectively. u,Curved-edge I42 thus is -a segment of the parabolalwhose equation is length'w of bases 4Il and' 45 to the length 2h of' edges 40'and 44.

Referring further to Fig. 3, aline l'is drawn parallel'to bases .4 I` and 45.,- Line'Z traverses opento Fig. 2, there is shown an 'enlarged elevation of i the screen 2'!) with the two substantially triangular openings 2| and 22. Opening 2I1hastwov straight edges 40 and 4I which areat right angles to Vone another, and. acurved edge` 42 opposite theiright angle formed by edges "43 and 4I".` Correspond'- ingly, opening 22 has two straight edges'44 and 45 which are at rig-ht angles to one another, and a curved edge 46 opposite the right angle formed lby edges 44 and 45. The particular manner` 'in which edges 42` and 45 are curved, will bedescribed presently. i

Openings 2l and22 are spaced apart horizon]- tally so as tobe separated by a distancej2d,at which distance straight edge 40 of opening 2'Iand straight edge 44of opening 22 are parallel to'one another, Straight edges 4I and 45 of'y openings 2l and 22, respectively, lare also parallel to one another, the distance between. edges `4I 'and 45 beingl equal to the length 2h of edges 40 and 44. Assuming that straight edges 4I and 45 are the bases of openings 2| and 22, respectively, the tip V of opening 2I thus is in alignment with the base 45 of opening 22, while the tip `W of Opening 22 is in alignment with the base 4I of opening 2 I. Curved edges 42 and 43, nally, aresegments of two parabolae which are equal, but'differently positioned. Edge 42 extends from tip V towards base 4I and is a segment of the parabola, opening `ings 2| and.22 so that segments AB andA CD are ,determined 'on it by edges 4I)r and 42 andedges .43.vand 44,respectively. Fig. 3 also shows that,

r.with respectt to Equationsl and 2,"AB. equals :r-dfor-fa' given V.value of y and CD Vequals fix-Hl) for. the same value of y. According to ,Equation 11,' therefore,

y,one line lthus is a linear function `of y, andr this `fact bears upon the operation of the opticalsystem of Fig.,1 as follows: I

f As has been` pointed .out hereinabove, the -images 25 and 26 formed in the plane of slit'21 are two uniformly4 illuminated light spots whose shape and relative position are those of openings 2I and 22,. Furthermore, screen 20 is adjusted so that bases 4I and 4,5 of openings 2l andf22, respectively,4 extend horizontally,` that is,- inthe same direction as mirror axis 349-34 andfslit 21. For thisy adjustment of screen 20, lineil of 4'3 indicates the horizontal line through openings 21 and 22 which is conjugate to slit 21 with respect 'to lens 23,V the position'ofthis line relative'f-to to the right, which has its vertex at V and its 75 `inclination of mirror I2. SegmentsAB'andfCD atome? 7 -onlineflg therefore,` represent-the two horizontal lines. of light'appearing .at slit2f'|, and recording point 30 fora given angleof rvibrationofmirror .|2.:1 Moreover, the adjustment .of mirror vI2 'is such that at its rest, or zero,rposition, that is, when no electrical impulses'are applied to oscillograph 33, line Z .isV halfway between gbases '4| and.45..so .as tocoincide with axis X-l-X. The term Equations 1, 2, andY 3, then `denotes the deflection, by the vibration'of mirror |2..ab.out its axis-34-34, of images :2:5and =2v6xwith respect to'slit Y2-`| in such a manner' that positive values of :y 'indicate deflection upwards, that is, in a sense opposite to that indicated 'by the arrow 32,

while negative values vof vy indicate deection f downwards, that is, in the sense indicated by arrow'32. According toEquationsland 2, the length of each of the two lines of'light .at slit 21 and recording point `3|) thus varies in proportion to the square of the deflection of images 25 .and 26, respectively, and the length of the one line Varies at the same rate as, but 180 out of phase in relation to, the length of the .other line. But, according to Equation 3, the difference in length of the two lines of light is a linear function of the deflection of images 25 and 26, and valso of ithe amplitude of the electrical impulses applied to oscillograph 33 since `the deflection of images -25 and 23 is proportional to this amplitude.

The two `variable area half-tracks 35 and 36 on iilm 3|, therefore, have modulated portions which are opaque and vary in this manner: The difference of their horizontal extensions, or widths, is a linear function yof the amplitude of the electrical impulses applied to oscillograph 33, Y

although their individual widths vary in proporincreases vwhen wz decreases .and vice versa.

tion to the square of that amplitude; the Width of the'opaque portion ofv half-track 36 varying at the same rate as, but V18.0 out of phase in rela- 'tion'to, the width of the' opaque portionof vhalftrack 35.

'The push-pull class A variable area trackV 3l whichis composedl of half-tracks and `36, may betra'nsferred from lm 3| `onto another `lln by printing. Such a print isillustrated, by way of example, in Fig. 4. A lm 5| has printed thereonthe push-pull class A variable area track 5,2,which is composed of the two 'half-tracks 53 andr 54 in juxtaposition. Track 52 jis'shownflike.-

wise by way of example, asbeing arecord ofthe full cycle of a sine-wave. This cycle is'completely recorded oneach vhalf-track 53 and 54, but vthe two half-tracksW are fdisplaced 180"out of phase in relation 4to one-another; the peak 55 on half-track 53 being opposite the val1ey7560n half-track 54 transversely'f jillrnY 5|, and the Avalley 51 on half-track 5,3 being, inthe same manner, opposite the peak 58 on half-track-54.

' Eachfhalf-track 53 yand 54 has an'opaque` portude,- thei difference y1in-wz is a'. linear functionY thereof. Since, furthermore vw1 and vary 75 tion 6| and 62, respectively. anda transparent "60 .Track '52 may be :reproduced with. any conventional push-pull reproducing system-Suona system essentially includesltwo photocellsene for eachhalf-track, which` generate voltages in 'a pu'shepull .electrical `.circuit 189 vout of. phase. track :'52 is ,thusv reproduced, v.a certain amount of riight flux is transmitted by transparent portion 63 to the one photocell, yand another amount of vlight flux ,byl transparent portion 64 to the Vother photocell. Since 4these twoV amounts of -Iig-ht flux are linearly related to w1 and wz, respectively, their difference is a 'linear function of the amplitude referred .toV above. So isy the response'of the entire reproducing system since it is, as is well knownfin the art, equa-l to lthe difference in response ofthe 'two'photocells A The yelectrical impulses applied to Yoscillograph 33, recorded on `film' 3|, andf printed onto film 5|, may thus begreproduced Without amplitude distortion although half-tracks 35 and 36, and half-tracks 53` and r54', are distorted because the Width of their individual modulated portions varies in proportion to the vsquare of the amplitude of said electrical impulses.

So far, it has been explained only thatundistorted vreproduction of the electrical impulses recorded with the optical system of Fig. l may beV X-X- For this position of une l, the segments AB and CD thereon become the segments AB and CD on axis X-X. The length of each segment AB' and CD is kh2, Vwhich value is ob` tained by substituting O for y in Equations l and 2 and solving them. for m-d and :c-l-d),

respectively. The differenceV in length of-segn' ments AB `and CD hence Vequals zero-which result' is also obtained by substituting O for y in Equation 3'-and so does the difference wr-wz when" the value of w1 and wz each becomes equiv- `alent to ML2. Thus, there actually is no response from half-tracks V53 and 54 when vmirror'jlis Vat rest.

Furthermore, the length kit? of 'segments and CTD is one quarter of the length w of bases 4`| and45' since w equals 4lch2. This result is obtained by Isubstituting -h forry in Equation .l and -i-h for y in Equation 2 and solvingV the two equations for -d and (-l-d), respectively. Y .Abroken line 48 is drawn from the tip V of opening 2| to the end point P oi. its base, 4|, and a broken line 49 from the tip W of ropening 22 to the end point Q of its base 45. Lines 48 and t 49 both are straight. There is determined, there fore, von axis X-X the segment AE by edge Vand line` 48, and the lsegment FD' by line 49'and edge 44. According to elementary geometry, the length .of segmentsA'E and FD' is half the length w of bases 4| and 45, that is, twice the length of segments A'B and CD.

The fact that the lengthv of segments AB'y and C'D'isY Y x 'Now it will bev shown wherein the 9 While the length of segments A'E landliD' is leadsto the following conclusionsi 'y t Let,V it be'assumed that,'in the opticalrsystem of Fig. 1, there are employed openings 2| and 22 and, alternatively, tv/o conventional openings Which are bounded .bythe straightedgesw, 4| and' 48, and 44, 45 and 49, respectively. Since the two'pairs of openings both have edges 4| and 45 as their bases, the maximum length Which each f the two lines of light at slit 21 and. recording point`3 may have, is the same in either case. But, when mirror |2 is at rest, the length of the two lines of light ishalf their maximum length with the two straight-edged openings, While it is reduced to one quarter of that length withvopenngs 2| and 22. The opaque portions of' half-tracks 35 and 36, and the transparent portions 63 and 64, therefore, may have the samemaximuml Width with either pair of openings.. But their Width for the rest position of mir-V ror |2 is half their maximum width with the conventional pair of openings, While it is reduced to a quarter of that width with the pair OffV Openings according to the invention.

The variable ar/a half-tracks 35 and 36, and 53 and 54, thus are characterized by the fact that their modulated portion h'as a Width Whose ezro value, th at is, the value for the rest position of mirror |2, is one quarter its maximum value, that is, 'the value vfor the maximum vibration of mirror I2.' This relationship between the zero and maximum values of the width of transparent portions 63 and` 64 becomes important whenjthe electrical impulses applied to oscillograph 33 are sound currents so that sound is to be reproduced from track 52 on lm 5|. Its establishment then effects a reduction of ground noise which amounts to 3 decibels. This result is sufficient to make 5' then is again i I0 tip V of opening 2| is iii-alignment with fthexbas'el 85 of opening 12 whose tip W' in its turn,'is,A infv alignment with the base 4I of opening 219.1.' @pen-- ings 2| andl 12 thus are alikebut inversely'positioned vertically. More particularly;I strziightL edges and 4| of opening! 'form a riglitan'gIe,A

and 'so do straight e'dges`84 and `85of`openingf 12. Curved edge 42 of opening 2|is opposite the right angle formed by'edges' 481and 4|",and curved edge 86 of openingv 12 is opposite the'right'. angle formed by edges84 and 85:- vTheA length of straight edges 48 and 84 is 2h,"that" fstraight edges 4| and'85 is w, and .curvededgesr42and' 86 are segments `of two parabolaefwhichiarerequal, but differently'positioned.` The parabola'y ojf'edgef 42, which opens tothe right,"hasmtsverteib-vat V and its axis a parallel'to' base4'lrrsof-thatffedge 42 extends from tip V towardsQbasM-. The pas; rabola of edge 8|opens-l also to the .riglitpbutfhasf its vertex at W and its axis-:bf paralleiito'ibase'-, 85 so that edge 86 extends from tip .W". ftoyvazrdsi base 85.

Finally, openings 2| and`12 are spaced apartJ horizontally inv such' a manner thatedges lll-and 84 are at thedistanceZd-l-w, parallel; to one an?, other, while the distance of tip Virom base 8 5 is Zdand thatV of tipW from ba'se 4 i'S'fZdlFr.

Openings 2| and 12 'are vrelated tof', system ofi rectangular co-ordinates with axes'X-TX Y-Y. Axis XMf-X is parallel' to bases" 4'| 'ay d' 85 and intersects edges 4l) and 84 at theirrnijdpoi i and axis Y-Y .is parallel to edges Mirar-111184, 1

spectively. The equation of parabolic edge 42 While the equation of parabolic edge 86 is the application or the electrical methods ofg ground noise reduction superfluous in a. great number of practical-cases so that the production of variable area soundtracks with' ground noise reduction is materially facilitated by the present invention.

As shown in Figs. 2 and 3, and described here-4 inabove, openings 2| vand 22 are inversely positionedvertically in that the tip of the one open` ing is in alignment 'with the base of the other opening, and vice versa. As' further shown in Figs. 2 and 3, openings 2| and 22 are inversely positioned also horizontally in that their` straight edges 4G and 44 face each other, While their parabolic edges 42 and 46 are turned away from each other and open in opposite senses. In other Words, openings 2| and 22 are arranged sympoints P and Q of their bases 4| and 45, respectively. This point coincides with the origin O in Fig. 3.

However, the factthat'openings 2| and 22'v have a center of symmetry, is immaterial as'far as th'e present invention is concerned. That is to say, the invention may be carried out also with pairs of openings Which are invertedonly' vertically. Two such pairs of openings are shown in Figs. 5 and 6 by Way of further example. Fig.

5 shows th'eopening 2| of Figs. 2 and v3 asso-I ciated 'with an opening 12. v The corresponding edges 40 and 84, 4|fand '85, and 42 and 86of openings 2| and 12 are of equal length, and th'e is again the length. ofthtwosegnrnts de 47ch2 being equal to w as has been pointedxoutfi` hereinabove. The diierence, therefore; ofi'the" two segments determined on line lb'yledges 40andf 42, and edges 84 and 86, respectively; aga-in equals -4lchy (Equation 3),- and it again rbec'omes zerii when line l coincides With axis"X.-'X; "'.The-length'' ofthe two'segments` is againkhz, or f:

in this case, while.'

mined on axis X-X by thesides of thetworight angled triangles Whose cathetes are. edgesl4`a11 l,w 4|, and edges84 and I85, respectiyel'y...

In Fig. 6, the opening 22 of Figsaanaais associated with an opening 1|.. The correspond# ing edges 44 and 80,' 45 land 8|., and .4B-,.andlf8 2 of openings 22 and 1| are of vequal length,"agie-- the tip W of opening 22 is in alignment.withthe base 8| of opening 1| Whose tip V-,-in its .turn-,fis

. in alignment with the base. 45 of. .opening 322:-,

Openings 22 and 1I thus are alike but. inversely., positioned vertically. L.

More particularly, straight edges 44 'andi 4'5``orj opening 22 form a right angle, and so do .str-aigl 1t.`

edges 80 and 8| of opening 1|. Curvedlfedgef,46.

and 80 is 2h, that of straight edges 45 and 8| of opening 22 is opposite thezrightfangle formed, by edges 44 and'45, andcurved. edge 82loffopn. ing 1| is opposite the right'.ang le.. foigrnedll.yiI edges and' I. The length of straight edges 44 is w, and curved edges 46 and 82 are segments of twozparabolae rwhich are equal, but-dierently positioned., Theparabola of' edge 46, which Operisi to: they left', .has its vertex: at W and'` its axis b parallel to base 4:5.1so that edge 46 extends from tip/QW towardsy base 45. The. parabola'of' edge 82 andoitsfaxis a parallel to basev 8| so thatedge f opens'also. .toy'thelef-a butv has its vertexgat V' 82"-'extends from tip-V towards base 8|'. Finally,

openings 22A and 'Il arev spaced apartk horizontally in'suchia manner that edges 44 and 88 are at the 1 distance2d+w parallel to one another;y while the distance. of: tipfW. from base 8| is 2d and that of Y tipY'f'from-'baseisi2d+wu Y 1 Openings .22. and 1li are related to a system of .fect'angularco-ordinates with axes X-X andv -Yjr Axis. X--X is parallel to bases 45. and 8| 11d-intersects edges 44 and 80 at theirrmi'dpoints,

idg-HL). 2:-, (ar-HZ) linel by edges-82 and 86, and-edges 46 and 44,

. respectively, again equals -47chy (Equation 3.)',

and: it again becomes zero when line'l coincides with. axis X-X. The length of the two seg'- .ments-is, againelehz, or

INS

in this case, wime is again the length of the two segments determined on axisnX-Xl by the sides of the two right-:angled triangles whose cathetes are edges 1 l 80y lgjand edges 44 and 45, respectively.

Openings 12 and 1|- which` have been shown in l Figs.; 5 and; 6jas associatedwith openings 2| and j 22, respectively, may also be associated one with 1 another as shown in Eig'. '7. "Openings 1| and: 12 1 are alike, as will be seen from the description of Figs. 5 and 6, and arranged so that the tip V of opening 1| is in alignment with the base 85 of i opening 12 whose tip W', in its turn, is in alignment with the base 8| of opening 1I. The two openings are spaced apart horizontally in such a manner that edges 80 and 84 are at the distance Zai-|2211) parallel to one another, while the disj tance' of tips V and W' from bases 85 and 8|,

respectively, .is Zd-l-w. Openings 1| and 12 thus are inversely positioned not only vertically, but al'sohorizontally.

Openings-TI and 12 are related to a systemV of rectangular cna-ordinates with axes X--X and Y-Y. Axis X-X is parallel to bases 8| and 85 is again the length ofl the two segments determined on axis X-X by the sides, of', thetwo: rightangled triangles whose cathetes areedges 88 vand 8|, and edges 84 and 85, respectively.

When the openings 2| and 'l2 of Fig. 5, th openings. 22 and 1| of Fig. 6, or the openingsv'll in this case, while and. 72 of' Fig. 7, are in the screenZ oi the .optie Vcal system of Fig. l, screen 2i] is` adjusted sothat bases 4| and 65, 45 and 8|, or8| and 85, extend horizontally. Also, mirror i2 isfadjusted so that, atits rest position, line Z is halfway between bases 4| and 85, 45 and 8|, or 8| and 85.l The optical system of Fig; l then operates in the manner described hereinabove in connection with openings 2| and 22.v In each of the cases illustrated in Figs. 5 to 7, therefore, the explanations aravalid which have previously been made as regards the variation'inlength .of the lines of lightat slit Y2l and recording point 38, andthe variation. inwidth of theopaque portions of half-tracks V `and 36, and of the transparent portions 63 and 64.v

More particularly, when a print is made of the push-pull class A variable area track produced on film 3| with any one of thegpairs-ofV openings shown in Figs.` 5 to.7, the track thusobtainedby printing has the general appearance of the track 52 illustrated in Fig. 4. The, track on such a print hence is .again composed of the two variable .area half-tracks 53 and` 54 which are complete, but displaced 180 out of :phase in relation to one another, and eachof the two ,transparent portions 63 and` 64 has again a width. whose zero value is one quarter its maximum value.'

The only difference between the tracksproducedby means of the various pairs of openings and intersects edges 80 and 84 at their midpoints,

and axis Y-Y is. parallel to edges 80 and 8'4, its distance from either edge being d+w. Parabolic edges 82 and 86 then are again the lines conforming to Equations 4 and 5, respectively. The difference, therefore, of the two segments determinedron line l by edges 82 and 80, and edges 84 i andi8'6-,1respectively, againequals -ilchy (Equationl, and it again becomes zero when line ZY coincides with axis X-X. The length of the. two segmentsis again Ich?, or

V33t..y and otransparent portions 63 and- 64.

the rvcase of openings 2| and 22, thestraight.V

is in the yrelative position of the straight boundaries of the opaque portions of half-tracks 35 and In boundariesrof. transparent portions 63 and. 64 c0- ipcide Vwith thev inner boundaries 6l. allot-.68, respectively, ofhali-tracks 53 and 54, as illustrated in 4. With openings 2| and l2, thestraght boundary of portion63 retains its position, while that of .portion 64 coincides with the outer boundf ary i8 of half-track 54. With openings 22 and 7|', theV straight boundary of portion l6.4,has the position illustrated in Fig. 4, while that of portion 63- coincides with the outer boundary 69. of half-v track 53.v With openings 1| and 12., finally, the

straightboundaries of portions 63 and 54 coincidek with outer boundaries 69 and 10, respectively.

The straighthoundaries of the opaque portions of half-tracks 35 and 38 correspondingly change their position since it, too, depends upon the difference in position, relative to each` other, of vertical edges 48 and 44 4U and 84, 44 and 80, and and 84, as illustrated in Figs. 2 and 5 to 7.

The openings shown in Figs. 2 and 5 to 7 all have a shape which is derived from a rightV triangle.

ble area tracks as illustrated in Figs. 1 and 4. The invention, however, may also be employed when it is desired that the push-pull Class A tracks on films 3| and 5|, respectively, be composed of two variable area half-tracks ofthe bilateral, or symmetrical, type. To achieve this end, there must be employed in screenvZJ two When, therefore, theseA openings are in the screen 20 of the optical system of Fig.. 1, the half-tracks 35 and 36 on lm 3| and the half-, tracks 53 and 54 on nlm 5|, are unilateral variaopenings vwhose shape is derived from anfisosceles triangle, such as the openings 90 and 94 shown in Fig. 8 by way of'exam-ple. y

Opening 90 has a straight edge 9| and is sym# metrica] with respect to the line RV1 which is perpendicular to edge 9| at its midpoint R. The curved edges 92 and93 of opening 90 extend from V1 towards edge9 I 'and arejsegments of two equal parabolae whose vertices are at V1.1and whose axes a1 and a2', respectively, are iparallel to Vedge 9|. The two parabolae, however, open in opposite senses, the parabola'of edge 92fopening to the right and that of edge 93 `to the left.

Similarly, opening 94 has a straight edge 95 and is symmetrical with respect to the line SW1 which is perpendicular to edge 95 at its midpoint S. T he curved edges 96 and 91 of opening 94 extend from W1 towards edge 95 and are Vsegments of two parabolae which are equal to one another, and also to the parabolae of edges 92 and 9,3. The parabolae of edges 96 and 91 have their vertices at W1 and their axes b1 and b2, respectively, parallel to edge 95. They open, however, in opposite senses, the parabola of 4edgeySS opening tothe left and that of edge 91 to the right. e 1

The distance of the tips V1 and W1 from th bases 9| and 95 of openings 90 and 94, respec` tively, is 2h. Since, furthermore, the four parabolae whose vertices are at V1 andgW1 respectively, are equal, bases 9| and 95,are of equal length (w). Openings 90 and 94, which thus are alike, are arranged so that the tip V1 of opening 90 is in alignment with the base 95 of opening 94 whose tip W1, in its turn, yis in alignment with the base 9| of opening 90. The two openings are `spa/ced` apart horizontally 1n such a manner that bases 9| and 95 are at the distance 2h parallel'to one another, and that the distance of tips V1 andgWi from bases 95 and 9|, respectively, .is 'f The co-ordinates of tips V1 and W1 then are respectively, or (d+2lch2, h) and respectively. This substitution of 27th2 forA is based on the assumption that w in the case of openings 90 and 94 equals win the case of openings 2| and 22, and in the latter case w is equal' to 4kh2 as has been shown hereinabove. i l

A comparison of Figs. 8 and 9 with Figs. 2 and 3, furthermore, reveals that the normalsRVi and SW1 and the straight edges 40 and 44 have the same length (2h) and are the tangents at the vertex of the respective parabolae in each case.

is drawn to a somewhat larger4 escu i ou

r4' But the distance of parabolic edg"e's92 `andV 93 v'from the normal RV1, and that of yparabolic 'edges9'6 i and 91 from the normal SW1, is

at bases9| and 95,1respectively, while.tlrne'rli-s-v A tance of parabolic edge 42 fromstraightiedge 40, and that of parabolic edge' 46 from straight "edge 44, is w at bases 4| and 45, respectively. This condition makes it necessary to reduce the factor of proportionality k in Equations 1 and 2 by one half in the equations for-parabolic edges 92,- 93; 96,and.91. y j i The `equation of parabolic. edge 92 thus is .a

that ofy parabolic edge 93 and that of parabolic edge 91 AK and KB, and segmentCD is divided by the normal SW1 into thetwo equal segments CL and.

LD. 9 also shows that, for the same value of y, segments AK,`KB,.CL, and LD, Aare equal to the right members of Equations 7, 6, 8, and 9,v

respectively. According to Equation '7, therefore,

The difference of the two segments and CD" on line l hence v'is again alinear function of yl since again (3) -AB-'fcngikny When, in the caseof Fig. 9, line l coincides..

with axis X-X,.seg1ments AB and CDbecme segments AB and CD, respectively, asin the case of Fig. 3. But segmentA'B' now isco-m-v posed of, the two equalsegments AGand GB',

' and segment CD of the two equal segments CH staand Huus- 'f f 15 and y ,'Iherlengthrof 'each segment AG.,G1Bf`,

which value is obtained by substituting O for y in Equations 6 to 9 and solving them for their right mem-bers. The length of segments A'B'- and-07D' thus lis again kh2, or J that is, half the length of theA two segments MEy and 'FN which are 'determined on axis. by the sides lof the two iscsceles triangles with bases 9| and 95, and tips V1 and W1, respectively;

When openings 90 and 94 are in the screen 20 of the optical system of Fig.'1, screen 20 is ad-` justed so that bases 9| and, 9.5 extend. horizon`V tally, and the adjustment of mirror |2 is such that, at its rest position, line Z is halfway between bases 9| and 95. 'Ihe push-pull class A `track produced on film 3| then is composed of X4-X, respectively,` represent different values of the' horizontal extension, or width, of openings 2|, 22, 1|, 12, S0, and 94, respectively. Since, furthermore, the lengthof those bases and segmentsfis equal to the right members of Equations l, 2, and 4 to 9, for certain values of y, the width of the openings increases infproportion to the square of its distancel from their respectiveftipsv Vtion V,contemplates their employment `also withv the horizontal extension, or width, of the individual opaque portions of the twosymme'trical half-tracks varies. in proportion to the square ofthe amplitude of the `electrical impulses ap-` plied to oscillograpl'l` 33, but the difference inv widthV of the two opaque. portions isr a, linear function, of thatamplitu'de Also, the zero value of this widthis onequarter lits maximum value since the length of segments AB and CD' is one quarter the length w of. bases 9| and S5.

When the push-pull class Asymmetrical variafble area track produced. on lm 3| by means of Openings 90 and 94 is transferred onto film 5|. by printing, the resultant print has the general yappearance of the track |02 shown in Fig. 10;

Like track 52track |02 is illustrated as being a record of the full cycle of a sine wave. This cycle is completely recorded on each of the two half-tracks |03 and |04 which compose track |02,

' but half-tracks |03 and`|04 aredsplaced 180.`

parent portion |09 which divides its opaque portion into the two portions||a and ||0b. Finally, the widths w1 and f of ytransparent portions` |06 and I 09, respectively,

vary each inproportion to the square of the amplitude of the electrical impulses applied.` to oscillograph 33, while the difference wi-wa is a linear function of that amplitude; the zero value of 'w1 Vand wz being one quarter their maximum value.

lIn lview of the foregoing explanations of Figs.

2, 3, and to 9, it will be understood by those. skilled in lthe art that the bases 4|, 45, 8|, 85, 9|., and 95, and the'segmentson line Z and 'axisI vor,

certain variable density recording optical sys-L optical system of Figs. 11 to 13 differs from thatof Fig. 1 only in that the. microscope objective |4 and the spherical lens l5 of the4 latter `optical system have been replaced in the former optical .system by a cylindrical lens H4 whose cylinder.

axis.` is horizontal, andv a pair of beam-splitting spherical lenses ||5 Yand -||6, respectively. A

front'elevation of lenses ||5 and-||6 is-.shownirr Fig. 14;-

f Cylindrical lens Us forms, by its action. in the vertical plane,.at recording point.,|30 an image.

of the two horizontal lines'of light ,appearing at slit 21, while spherical" lenses ||5 and H6 form,

by their action in the horizontal plane, at the. same position vtwo, distinct images of mirror l2.. There thus are produced at recording pointl.

twohorizontal 'lines of light in juxtaposition The length of these two lines of light is constant,

but their intensity may continuously be varied in accordance with the amplitude Vof theelectrical impulses applied. to Voscillo'graph 33. Since, in all otherrespects, the optical system of Figs..11 to 13 operates in the same manner as the variable density recording optical system shown in Figs, 1 to 3 of my U. S. Patent No. 2,312,259, granted Feb, 23, 1943, reference is made to that specification by way of further explanation.

When, therefore,as shown by way of example in Fig. 11, openings 2| and 22 are employed in the screen 20 of the optical system of Figs. 11 to 13, the intensity of each of the two horizontal lines of light at recording point |30 varies in proportion to the squareof the amplitude of the electrical impulses applied to oscillograph 33, while the ,difference in ,intensityof -the'tw'o` lines of light is a linear function thereof. As lm 3| moves vertically past recording point |39, there is thus produced thereon a photographic record of the electrical impulses applied to oscillograph eachtrack r|35 and |36 lis, a complete record of' On account of the inthe electrical impulses.- verted position of openings 2| and 22, however, track |36 is displaced 180 out of phase inrela- |35 and |36;- in juxtaposition.,Y

tion to'track |35 transversely of lm 3| so that tracks |35 and |36 are the component ,halftracks of a push-pull class A variable density track |31.

The methods of producing the variable density track |31 and the variable area track 31 thus both involve the following steps: Two horizontal lines of light are produced in juxtaposition at recording points 30 and I 30, respectively. The amount of light flux contained in each line of light is continuously varied in proportion to the square of the amplitude of the'electricalimpulses applied to oscillograph 33, but the one amount of light flux is varied 180 out of phase in relation to the other amount of light flux. The variation of the two amounts of light flux is accomplished by varying either the length of the two lines of light, or their intensity. Track 31 is obtained in the first case, and track |31 in the second case. It is well known in the art that any kind of sensitive emulsion with which lm 3| may be coated,respon'ds linearly not to its exposure, but to the logarithm thereof. The variation in density, therefore, of half-tracks |35 and |36 is not 'proportional to the square of the amplitude of the electrical impulses applied to oscillograph 33, although the variation in intensity of the two lines of light at recording point |30 is so proportional. But, for making a print of track A|31 there may be employed methods, generally known to those skilled in the art,'by which the complete photographic process is controlled so that the light transmission of the print is proportional to the exposure of lm 3|.

VA print obtained in this manner is illustrated, y.

by way of example, in Fig. 15. This figure shows, vprinted on lm 5|, a push-pull class A variable density track |52 which is composed of the two half-tracks |53 and |54 in juxtaposition. Like tracks 52 and |02, track |52 is assumed to be a record of the full cycle of a sine Wave. This cycle is completely recorded on each half-track v| 53 and |54, but the two half-tracks are displaced 180 out of phase in relation to one another.V That is to say, the region |55 of largest light transmission on half-track |53 is opposite the region |56 tof smallest light transmission on half-track |54 transversely of film 5|, and the region |51 of "smallest light transmission on half-track |53 is, in the same sense, opposite the region |58 of largest light transmission on half-track |54.

Since track |52 was obtained by theV photographic methods referred to above, its light transmission is proportional to the exposure of lm 3| which, in its turn, is proportional to the intensity of the two lines of light at recording point |30. The light transmission of each half-track |53 and |54 hence varies in proportion to the square of the amplitude of the electrical impulses applied to oscillograph 33, while the difference in ,light transmission of half-tracks |53 and |54 is a I trical impulses recorded thereon is undistorted for the reasons set forth hereinabove in connection with the description of track 52. Also, when those electrical impulses are sound currents, a rereproduced from track |52. 'Ihis reduction is due to the fact that, on account of the shape of openingsw2| and 22, each half-track |53 and |54 has a light transmission whose zero value is one quarter its maximum value the zero and maximum values of the light transmission of half-tracks |53 and |54 being its values for the restposition of mirror I2 and its maximum vibration, respectively.

The ground noise reduction obtained by the employment of openings 2| and 22 in the optical system of Figs. 11 to 13 amounts Yto 6 decibels. This-result is sufcient to make the application of the electrical methods of ground noise reduction superfluous in a great number of practical cases. The4 production, therefore, of variable density sound tracks with ground noise reduction isV materially facilitated by the present invention.

In the place of openings 2| and'22 there may be employed in the screen 20 `of the optical system of Figs. `11 to 13 also the openings 2| and 12 of Fig. 5, the openings 22 and 1| of Fig. 6, the openings 1| and 12 of Fig. '1, or the openings 90 and 94 of Fig. 8. Substitution of any of the pairs of openings *shownV in Figs. 5 to 8 for openings 2| and 22, however, does not aiect either the appearance, or the properties described hereinabove, of half-tracks |35 and |36, and |53 and |54, respectively. In all cases, there are produced at'recording point |30 two horizontal lines of light of constant length whose intensity varies in proportion to the square of the amplitude 0f the electrical impulses applied t0 oscillograph 33. y

In considering Fig. 15, Iinally, it should be borne `in mind that the Variation in light transmission of a variable density track can be illustrated only by diierences in its shading, and that it is wellnigh impossible properly to indicate, in a shading made by hand, the particular variation in light Vtransmission which half-tracks |53 and |54 have in accordance with the present invention. Actually, the variation in light transmission of halitracks |53 and |54 is the exact counterpart of the variation in width of transparent portions 63 Aand 64 as diagrammatically illustrated in Fig. 4. Fig. 15 hence is merely a crude illustration of the push-pull classV A variable density track |52.

In an actual embodiment of the optical systems of Figs. 1 and 1l to 13, thedimensions of the images on screen 24 may be different from those of the openings in screen 20. Such enlargement or reduction, which depends upon the ratio of imagery chosen for lens 23, `does not affect the validity of the explanations made hereinabove, since it doesnot involve a change in proportion.

Tracks 52, |02, and |52, lare shown in Figs. 4, 10, and 15, and have been described hereinabove, as printed from iilm 3| onto ilm 5|. But these tracks may be produced also immediately on lrn 37| by adapting the optical systems of Figs. 1 and l1 to 13 for recording in accordance with the reversal method. Y y

When the amplitude oi the electrical impulses applied to the oscillograph 33 of the optical systems of Figs. l and 1l to l3'is very large, the images on screen 24 may be deflected to such a :degree that their tips and-bases cross slit 21. This ditional opening, or openings, of suitable shape in suchl a manner that the .two ormore openings yform a single opening whose shape is again substantially triangular. .itself is rwell known inthe art, is illustrated, byr

This expedient, which. in

duction of groundnoise is effected when sound `is :75 .way of example, in Figs, 16 and 17 as applied@ 519 openings 2| and" 22, and openings 90 and 94, respectively.A I f Fig. 16 shows how, inY order to obtain the de- 'sired'r'esult, opening2| may be combined with the two-rectangular openings |6| and |62, and opening 22 with the two rectangular openings |63 and |64, so'v as to form the substantially triangular openings |2| and |22,` respectively. IOpenings Av|^6| and |63 are equal, and so are openings |62 and |64. Openings 2|, IGI, and |62, are varranged so that one of the vertical edges of'opening |6| coincides with the vertical edge 40 of opening 2|. Since, however, this edge'of opening |6| is longer `than edge 40, its portion |65 extends beyond the arranged so that vone of the vertical edges of opening |63 coincides with the vertical edge 44 of open- 'ing 22. Since, however, this edge of opening |63 is longer than edge'44, 'its portion |61 extends beyond the tip W of opening 22. One of the horizontal edges of opening |64,'onfthe'other hand, coin'cideswith the base 45 of opening 22 and the horizontal edge |63 of opening |63.

v TheA transtion'from the parabolic edges 42 and 46 of openings |2| and |22, respectively, to their straight edgesA |65 and |61, respectively, is a smooth one because Vedges |35 and |61 are the tangents at the vertices of parabolic edges 42 and 46, respectively. Y 1

In Fig. 17, opening 90 is combined with openings |6| and |62, and-opening 94 with openings |63 and |54, so as to form the substantially triangular openings |90 and |94, respectively.

Openings 90, |6l, and |62, are arranged so that opening 6| bisects opening 95. Opening 90 is thereby divided into the equal portions 93a and '90b with bases 9|a and 9|b and tips V2 and V3,

, with bases 91a and SIb, and the horizontal edge Correspondingly, vopenings 94, |63, and |614, are arranged so that opening |63 bisects opening 94. Opening 94 is thereby divided into the equal portions 94a and 94h with bases 95a and 951) and tips W2 and W3, respectively, and the portions |13 andV |14 of the vertical edges of opening |63 extend beyond tips W2 and Wa, respectively. Opening |64, onthe other hand, has a horizontaledge which coincides with bases 95a and 95h, and the horizontal edge |68 of opening |63. I

The transition from the parabolic edges 9 2 and 93, and 96 and 91, of openings |90 and |94, respectively, to their straight edges 1| and |12, and |13 and |14, respectively, is a smooth one because edges |1V|, |12, |13, and |14, are the tangents at the vertices of parabolic edges 92, 93, 95, and 91, respectively. i

lWith openings such asopenings 2| and 22, an

, 90 and 911|,Y their total width is utilized for varying thev two amounts of light flux passing through the slit 21 'of the optical systems of Figs. 1 and 11 to 13.A With openings such as openings |2| and |22, andv |90 and |94, however, that part'of their width which is 'equal to the horizontal extension, or width," of openings |6| and |63, respectively, vdoes not eiect a Vvariation of the light flux since 'it is constant. The effective Ywidth 'of the latter openings hence is the diiperence between their 20 total widthand the width-of openings |6| rand |63, respectively, so that it isequal to the-total width of the 'former openings. The eiective width of all openings thus is proportional tothe square of its distance'from Vtheir tips. But Vthe total width of all openings increases in proportion tothe squarey of its distance from theirtips, no matter whether it is equal to, or larger than, their effective width. It is understood, of course, that in the cases illustrated in Figs. 16 and l', the tips ofthe openings are rectangular rather than punctual as they are in the cases illustrated in Figs. 2 and 5 to'8, l Y

It will thus be seen, when openings-such as openings |2| and |22, and |90 and |94, are in the'screen 26 vof the optical systems of Figs; 1 and 11 to 13, the amount of light ux contained in each of the two horizontal lines of ylight at recording points r30 and |30, respectively,'is continuously variedl again in proportion to the square of the amplitude ofthe electrical impulses applied to oscillograph 33. In 'case suchopenings are employed'with the optical system of Fig. "l, thereiorethe push-pull class A tracks recorded on kfilm 3|, and the prints m'ade of these tracks on film 5|, are composed of two variable area half-tracks, and each half-track has a`modulated `portion whose width varies again in proportion to the square of that amplitude. However, lsince a part of the width of the openings here under discussion is constant, a part of the width of this modulated portion is constant, too. The modulated portion hence has now an eiecl tive width which is equal to its total width less the constant partv thereof. This effective width is proportional to thev square of the amplitude referred to above and its zero. value is one-quarter its maximum value, Vas in the case of the modulated portion yof half-tracks 35 and 36,53 and l54, and |03 and |04, whose effective width is equal to its total width.

In case openings such as openings |2| and |22, and and |94, are employed with the optical system oi Figs. 11 to 13 and prints are made on film y5| of the push-pull class Atracks recorded on iilmf3l, and in accordance with the photographic methods Y mentioned hereinabove, the prints are composed of two variable density halftracks, and each half-track has alight transmission which varies again in proportion to the square of the amplitude of the electrical impulses applied to o scillograph 33. However, since apart of the width of the above'openings V'is constant, a part of this light transmission is constant, too. The variable density half-tracks hence have now an eiective light transmission which is equal to their totaljlight transmission less its constant part. This effective light transmission is proportional to the square of the'amplitude rferredto above, and its zero value is one-quarter its maximum value, as in the case ofY half-tracks |53 and |54 whose effective light transmission is equal to their total light transmission.

Having thus described several embodiments of my invention, `I wish to point out thatfit is not limited to the specic structures shown, but is of the scope of the appended claims; f

What I claim is:

1'. The method of producing on a film a photographic record of electrical impulses whichincludes moving said 'lm past a recording point in a substantially vertical direction; producing at said 'recording point 'two h'o'rizontal lines of 4light in'juxtaposition,"'each of `'s'a'i'd 't'wo"linesfof a substantially vertical direction; producing atY` said recording point two horizontal lines of light in juxtaposition, each of said two lines of light being of variable length; and continuously varying said length in proportion to the square of the v amplitude of said electrical impulses, but varying the length of the one of said two lines of light 180 out of phase in relation to the length of the other line of light.

3. A photographic push-pull class A track on a film; said track being a record of electrical impulses, and composed of two variable area halftracks displaced 180 out of phase in relation to one another transversely of said film; and each of said half-tracks being a complete record lof said electrical impulses, and having a modulated portion whose width varies in proportion to the square of the amplitude of said electrical impulses.

4. A push-pull class A track according to claim 3 and in which said modulated portion is opaque.

5. A push-pull class A track according to claim 3 and in which said modulated portion is transparent.

6. A photographic push-pull class A track on a film; said track being a record of electrical impulses, and composed of two variable area halftracks displaced 180 out of phase in relation to one another transversely of said film; and'each of said half-tracks being a complete record of said electrical impulses and having a modulated portion whose effective width is proportional to the square of the amplitude of said electrical impulses, the zero value of said width being one quarter its maximum value.

7. 'I'he method of producing on a film a, photographic record of electrical impulses which includes moving said film past a recording point in a substantially vertical direction; producing at said recording point two horizontal lines of light in juxtaposition, each of said two lines of light being of variable intensity; and continuously varying said intensity in proportion tothe square of the amplitude of said electrical impulses, but varying the intensity of the one of said two lines of light 180 out of phase in relation to the intensity of the other line of light.

8. A photographic push-pull class A track on,

a film; said track being a record of electrical impulses, and composed ofy two variable density halftracks displaced 180 out of phase in relation to one another transversely of said film; and each of said half -tracks being a complete record of said electrical impulses, and having a light transmis'- sion which varies in proportion to the square of the amplitude of said electrical impulses.

9. A photographic push-pull class A track on a film; said track being a record of electrical impulses, and composed of two variable density halftracks displaced 180 out of phase in relation to one another transversely of said film; and each 22 of said half-tracks being a complete record of said electrical impulses and having an effective light transmission which is proportional to the square of the amplitude of said electrical impulses, the zero value of said light transmission being one quarter its maximum value.

10. A photographie .push-pull. class A track on a film, said track being a record of electrical impulses, and composed of two half-tracks displaced 180 out of phase in relation to one another transversely of said film; and each of said half-tracks being a complete record of said electrical impulses, and having a light transmission which varies in proportion to the square of the amplitude of said electrical impulses.

ll. In an optical system, a screen having two openings which are substantially triangular and alike; each of sadtwo openings having a tip, and a horizontal extension which increases in proportion to the square of its distance from said tip; and said two openings being spaced apart horizontally and inversely positioned vertically.

12. In an optical system, a screen having two openings which are substantially triangular and alike; each of said two openings having a tip,

and an effective horizontal extension which is proportional tothe square of its distance from said tip; and said two openings being spaced apart horizontally and inversely positioned vertically.

13. In an optical system, a screen having a first opening and a second opening, said first and second openings being substantially triangular and alike; said first opening having a first tip,

and a first horizontal extension whichinoreases in proportion to. the square of its distance from said first tip; said second opening having a second i tip, and a second horizontal extension which increases in proportion to the square of its distance from said second tip; said first and second horizontal extensions increasing at thegsame rate; and said first and second openings being spaced apart horizontally and inversely positioned vertically.

14. In an optical system, a screen having a first opening and a second opening, said first and second openings being substantially triangular and alike; said first opening having a first tip, and a first effective horizontal extension which is proportional to the square of its distance from said first tip; said second opening having a second tip, and a second effective horizontal extension which is proportional to the square of its distance from said second tip; said first and second horizontal extensions being equal; and said first and second openings being spaced apart horizontally and inversely positioned vertically.

15. In an optical system, a screen having -a first opening and a second opening; said-first opening having a first tip, a first base, and a first width which increases in proportion to the square of its distance from said first tip; said second opening having a second tip, a second base, and a second width which increases in proportion to the square of its distance from said second tip; said first and second widths increasing at the same rate; said first and second bases being equal; said first tip being in alignment with said second base; and said second tip being in JOI-IN A. MAURER, JR. 

